Scientists equipped with giant lasers have blown up gold at SLAC National Accelerator Laboratory, heating it to 14 times its boiling point. For a chilling second, they thought they broke physics, but they fortunately did no such thing. That said, they broke something else: a decades-long model in physical chemistry having to do with the fundamental properties of matter.
In an experiment presented today in Nature, researchers, for the first time ever, demonstrated a way to directly measure the temperature of matter in extreme states, or conditions with intensely high temperatures, pressures, or densities. Using the new technique, scientists succeeded in capturing gold at a temperature far beyond its boiling point—a procedure called superheating—at which point the common metal existed in a strange limbo between solid and liquid. The results suggest that, under the right conditions, gold may have no superheating limit. If true, this could have a wide range of applications across spaceflight, astrophysics, or nuclear chemistry, according to the researchers.
The study is based on a two-pronged experiment. First, the scientists used a laser to superheat a sample of gold, suppressing the metal's natural tendency to expand when heated. Next, they used ultrabright X-rays to zap the gold samples, which scattered off the surface of the gold. By calculating the distortions in the X-ray's frequency after colliding with the gold particles, the team locked down the speed and temperature of the atoms.
The experimental result seemingly refutes a well-established theory in physics, which states that structures like gold can't be heated more than three times their boiling point, 1,948 degrees Fahrenheit (1,064 degrees Celsius). Beyond those temperatures, superheated gold is supposed to reach the so-called “entropy catastrophe”—or, in more colloquial terms, the heated gold should've blown up.
The researchers themselves didn't expect to surpass that limit. The new result disproves the conventional theory, but it does so in a big way by far overshooting the theoretical prediction, showing that it's possible to heat gold up to a jaw-dropping 33,740 degrees F (18,726 degrees C).
“We looked at the data, and somebody just said, ‘Wait a minute. Is this axis correct? That's…really hot, isn't it?” Thomas White, study lead author and physicist at the University of Nevada, Reno, recalled to Gizmodo during a video call.
To be fair, this superheated state lasted for a mere several trillionths of a second. Also, it blew up. But that's still “long enough to be interesting,” White said, adding that “if you could prevent it from expanding, [theoretically speaking] you could heat it forever.” To which he added: “I'm very thankful that I get to blow stuff up with giant lasers for discoveries. And that's my job, you know.”
This conjecture will have to withstand follow-up experiments with both gold and other materials, White noted. But from a practical standpoint, the superheated gold kept itself together long enough such that the team was able to directly capture its temperature using their new technique, Bob Nagler, study senior author and staff scientist at SLAC, explained to Gizmodo in a video call.
“Actually, it's a funny thing; temperature is one of the physical quantities that humans have known for the longest time—but we don't measure temperature itself,” Nagler said. “We measure something that temperature influences. For example, a mercury thermometer measures how temperature changes the volume of a blob of mercury.”
This could pose a problem when studying some real-life examples of hot, dense matter in extreme states, such as the center of a star, the nose cone of a spaceship, or the insides of a fusion reactor. Knowing the temperature—a fundamental physical property—of matter in such situations could greatly inform how we investigate or, for the latter two, manipulate them to our benefit.
Often, however, these systems operate on temperature-dependent variables that are difficult to gauge, Nagler said. Technically, you could reproduce them in labs, but they'll “very quickly explode,” he noted—notwithstanding the fact that you'd still have to know the real-life temperature of the system being replicated to ensure the experiments are valid.
“So you have a chicken-and-egg problem,” he said. That's why the scientists are eager to inspect how their new technique could help in this regard.
“That's the most exciting thing about this work—we now have a thermometer for all these crazy experiments we've been doing,” White said. For example, the National Ignition Facility at the Lawrence Livermore National Laboratory uses a gold cylinder to contain their nuclear fusion experiments, firing X-rays at this cylinder to drive the fusion reactor, White explained.
“But we're also thinking of doing directly fusion-related experiments now,” he said. “To recreate fusion conditions, or the materials that make the fusion reactors, and just measure their temperature—which, actually, has been a long-standing question [in physics].”
The team is already applying the technique to other materials, such as silver and iron, which they happily report produced some promising data. The team will be busy over the next few months analyzing what these metals could be telling us, the scientists said. The project, for sure, is in full ignition.
